1. Field of the Invention
The present invention relates generally to windshield wiper systems and, more particularly, to a windshield wiper system that utilizes a single drive motor having a bellcrank linkage that is disposed between tandem windshield wipers.
2. Description of the Related Art
Windshield wiper systems commonly employed in the related art include pivotally mounted wiper blades that are oscillated across a windshield between an in-wipe position, typically located near the cowl of an automotive vehicle, and an out-wipe position, usually associated with an A-pillar on the vehicle, in the case of the driver side wiper blade in this representative example. It is typically desirable to maximize the angular velocity of the blade assemblies between the in-wipe and out-wipe positions where the blade assembly is moving across the windshield in front of the driver to reduce the duration of each wipe cycle. On the other hand, it is also desirable to limit noise and inertia loading by reducing the velocity of the blade assemblies as they approach the wipe limits. These are two competing objectives that must be balanced in order to be successfully and economically obtained.
One long-standing design approach that has been employed in the related art includes the use of a single motor assembly, driven in one rotational direction, driving two separate wiper arms across the windshield of a vehicle. This approach requires a fairly complex linkage system to convert the singular angular motion of the wiper motor into the two-way linear reciprocal motion to drive both wiper arms. In the dashboard-firewall area, where these systems are typically installed, this mechanical linkage required a large amount of underhood space. Moreover, the area near this moving linkage must be kept clear of wires and other vehicle components. Additionally, the moving linkage, with its several pivot and rotational points is subject to mechanical inaccuracies and wear, readily introducing excessive wiper movement.
Nevertheless, for many years, designers and manufacturers were reluctant to depart from this established approach. However, improved vehicle aerodynamics that have fostered vehicle designs having longer sloped front surfaces are leading to windshield designs with more pronounced rake angles that result in larger window surfaces. A wiper system for such windshields must therefore include longer, more massive wiper arms and blades to wipe the required percentage of the larger surface. This has created a number of problems. Most notably, the larger arms and swept surface area increases the size of conventional wiper systems to such an extent that it becomes difficult to fit a single motor system within the typically allotted underhood space. This problem is further aggravated by the same aerodynamic sloped front surfaces of the newer vehicle designs, which reduce the available underhood space. Additionally, the larger area to be swept by the wiper system requires more power and control over the wiper arm that can be provided by a linkage type system.
In response to the changes in vehicle front face design and the loss of available underhood space, the dual motor wiper system has evolved. Representative examples of such systems can be found in U.S. Pat. No. 4,585,980 to Gille et al., U.S. Pat. No. 4,665,488 to Graham et al., U.S. Pat. No. 4,900,995 to Wainwright, and U.S. Pat. No. 5,252,897 to Porter et al. These wiper systems are generally directly driven. Additionally, U.S. Pat. No. 5,355,061 to Forham employs a brushless DC motor to operate a direct drive windshield wiper system, as do others that follow. The more recent tandem wiper blade systems employing dual motors have utilized some hardware and/or software controlled switching scheme to control each individual motor, in reference to the other, to provide blade control across the windshield and prevent blade-to-blade contact.
Conventional tandem wiper systems use high-speed DC motors. This is undesirable, as it requires large counter-rotational forces to stop and then reverse the wiper arm at the end of its sweep. Also, large current draws are necessary to produce the counter-rotational forces which causes repetitive surges in the supplied power and induces great amounts of electro-magnetic interference to the immediately surrounding parts of the vehicle. With a high-speed DC motor, it is also problematic to vary the speed of the wiper arm as it sweeps across the windshield, if this is desired as part of a sweeping pattern or predetermined clearing scheme. These drawbacks stem from the conventional construction of tandem wiper motors, which have either a one-to-one direct drive or an inefficient gearing assembly to differ the wiper arm speed from motor speed. Thus, there is a need in the art for a direct drive motor for a windshield wiper system that is efficient and controllable at a lower drive speed and that is electro-magnetically clean.
One other drawback to conventional wiper motor systems has recently emerged. The conventional direct drive windshield wiper systems employ DC motors that are of the standard 12-volt operating standard. This is presently adequate, but current design trends are moving toward more efficient 42 volt based automotive electrical systems. The change over to a 42 volt automotive electrical systems will be highly problematic for the prior dual tandem wiper systems and presents a considerable drawback as the prior systems are not compatible. Therefore, there is a need to not only provide a tandem windshield wiper system that overcomes the above-mentioned drawbacks but that also has the ability to be employed in the newly emerging 42 volt automotive electrical system environment.
Additionally, there also remains a need in the art for a superior DC drive motor that can be employed in smaller vehicle applications having smaller windshields and an under cowl areas where space is limited. More specifically, there remains a need in the art for a single reciprocating DC drive motor of a type that satisfies the above mentioned needs and that can be employed with a bell crank and a pair of simple connecting arms to efficiently drive a tandem wiper assembly. Thus, not only is there a need in the art for a direct drive motor for a windshield wiper system that is efficient and controllable at a lower drive speed, is electro-magnetically clean, and has the ability to be employed in the newly emerging 42 volt automotive electrical system environment, but there also remains a need in the art for such a system that also can be efficiently employed as a single drive motor utilizing a bell crank linkage for a tandem wiper assembly.